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SMART PIXEL ARRAYSSPAsSHIVA MOHAMMADZADEH

JAN. 2015

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DEFINITION OF “SMART PIXEL”

• Integration of photo detector arrays and processing electronic logic circuits on a single semiconductor substrate

• Capable of performing parallel processing of large pixelated images by reducing a complex image into a manageable stream of signals

• Establish optical connections between input and output devices for many channels in parallel

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SMART PIXEL ARRAY

• A two dimensional array of optoelectronic devices

• Relates optical input and output with electrical process

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WHY SMART PIXEL ARRAYS?

• Suitable for board to board interconnections in digital systems

• The high space–bandwidth product (SBP) of optics

• Crucial to meet the demanding performance needs in high-speed switching ; optical interconnects in computers, and flat-panel display applications

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APPLICATIONS OF SPAs

• In the field of image processing, data processing, digital signal processing

• Many applications requiring high performance image capturing use SPAs, which integrate very special functionality at the pixel level

• The 3D image sensors consisting of SPAs are used to evaluate size, shape and volume in industrial automation applications

• SPAs are also used for optical data interconnect and optical memory access.

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PERFORMANCE

• The complexity of the logic operation in a pixel defines the smartness of that pixel

• Increasing the functionality of a pixel increases the area needed for the electronics

• “Granularity”, another criterion of smartness

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COMPONENTS

• Optical decoder

• Processing elements

• I/O Pins

• VCSEL Drivers

• Photodetector Array

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HOW DOES IT WORK?

• Multiple-quantum-well (MQW) modulators or vertical-cavity surface-emitting lasers (VCSELs) as the optical source

• Two approaches, monolithic and hybrid (e.g., monolithic VCSELs/GaAs and hybrid VCSELs/Si)

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WHY VCSEL?

• Because of the ability to form two dimensional arrays

• They are constructed out of material that is convenient for fabrication of photodetectors and logic circuits.

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VCSEL

• Substrate

• Layers of GaAs and AlAs the Bragg planes

• Quantum well region gain occurs

• p and n doped regions p-n diode junction

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ADVANTAGES

• High data-transmission rates through high-speed switching

• Decreased cross-talk, by virtually eliminating interference phenomenon

• Interconnects are lighter compared to today’s copper wires

• Provide high processing speeds by consuming significantly less optical power

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DISADVANTAGES

• Potential problems in combination of electronics and optoelectronics

• Fabrication of efficient light sources in silicon-based systems not mature enough

• GaAs based systems in electronic logic circuits are lagging behind silicon based CMOS technology

• The low efficiency of photodetectors results in reduced switching speed thus decreasing the data transfer rate

• Expensive

• Non-uniformity may result due to fabrication imperfections

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POSSIBLE APPROACHES TO SMART PIXEL FABRICATION

• Development of detectors and emitters based on indirect band-gap materials such as Si and Ge

• Epitaxial growth of GaAs or similar III-V semiconductor material on Si

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FUTURE

• To achieve more compact packaging leads to smaller components, shortens electrical connections within the SPA leading to higher potential speeds.

• To scale the SPAs to larger array dimensions.

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THANK YOU